I'm embarrassed to say I have been mailing my blocks incorrectly. I went to the PO, put the envelope on the scale and it said .44 -- regular stamp -- was the amount to pay. Yesterday I got one back saying it had insufficient postage. Today I went to mail the one that came back and another one (Star's) and I asked the postal clerk about it. She said it's not considered a letter, it's considered a package. This is the first time I've gotten one back, so I'm now concerned that some of the others I've sent have had postage due. If that is the case, I'm so sorry to those that received those blocks from me. At least I know now and won't do that again.